I"m not up on the latest stuff, homeless person that I am right now.
For years, half sized two strokes raced against double sized four strokes, with technology and advancements in materials winning out for the 4 strokes, as the 2's weren't being developed, a decision from whatever factors.
I used reed valves, and another kind of valve when I turned expert. Didn't really help, as it would indeed flatten out the powerband, but it also stressed the bearings, rings, cylinder walls, and gaskets LOTS more, with the major porting needed, cut pistons, and higher rpm to get the extra top end, since it seemed to add low/mid range. For an amateur like me, doing my own wrenching, I could race just as well for double the time using stock with port cleaning, jetting and airbox tuned to air conditions.
Sorry, my brain is confusing things. I used reed valves in motocross.
But I had a short stint at roadracing back in the late 60's, the rotary valve was what I meant.